The handling of particulate, granular or other flowable materials involves several problems. Such materials include chemicals, minerals, fertilizers, foodstuffs, grains, agricultural products and the like. Materials like these have generally been handled in two fashions.
Bulk handling equipment, including railroad cars, barges, trucks and the like, is employed when large quantities of material are required. Such bulk handling equipment, however, is of limited versatility. Only large quantities of materials can be handled efficiently, and only at those locations accessible to such equipment. In addition, sanitary standards are more difficult to maintain with bulk handling equipment because the materials are often exposed during at least part of the handling.
Container systems have been developed for handling relatively smaller quantities of material. The containers are individually filled, loaded for transportation to a point of distribution or use, unloaded, opened and emptied. Although containers can be more convenient in some respects, higher handling costs are usually incurred because less material is carried per container. The return freight costs of reusable containers can be substantial, particularly for rigid or noncollapsible containers.
There has been increasing interest in the use of flexible, collapsible containers for handling semi-bulk quantities of materials. The advantages of such receptacles include relatively low weight, reduced cost, better versatility, and low return freight costs in the case of reusable receptacles. One disadvantage of some flexible receptacles, however, is that they are not self-supporting and must therefore be handled with the aid of pallets or the like. Other flexible receptacles incorporate external sling assemblies for purposes of self-support. Two successful examples of receptacles with external sling constructions can be found in U.S. Pat. Nos. 4,113,146 and 4,143,796 to Williamson and Williamson and Derby, respectively. In other instances collapsible receptacles with integral sling structures, i.e., lift loops, have not exhibited adequate strength, particularly when a single lift loop is required to support the entire load contained by the receptacle.